In a substrate processing system, an atmospheric transfer chamber is provided between a substrate receiving vessel for receiving substrates and a substrate processing chamber maintained in a predetermined vacuum state, and a substrate held by an arm or the like is transferred between the substrate processing chamber and the substrate receiving vessel. In the substrate processing chamber, predetermined processing, e.g., reactive ion etching (RIE) or the like, is carried out. The substrate receiving vessel is referred to as, e.g., a carrier or the like.
In the processing chamber, a seasoning process or a cleaning process is performed before, after, or during processing product wafers. The timing for performing a cleaning process is generally set in a recipe. Therefore, a control unit for controlling the substrate processing system performs a cleaning process or a seasoning process by using a dummy wafer (e.g., a cleaning wafer or a seasoning wafer) based on the recipe before, after, or during processing of product wafers.
Dummy wafers are received in a dummy wafer carrier. Meanwhile, product wafers on which actual processing such as etching or the like is performed are received in a product wafer carrier.
The cleaning process is performed to remove deposits in a processing chamber by using a dummy wafer (herein, a cleaning wafer) after a certain number of product wafers are processed. Japanese Patent Application Publication No. 2007-250791 describes a unit for performing proper cleaning in accordance with processing types.
The seasoning process is performed to control a temperature in the processing chamber or a state of deposits adhered to an inner wall of the processing chamber by using a dummy wafer (herein, a seasoning wafer) after the cleaning process. Japanese Patent Application Publication No. 2007-266410 describes a seasoning process for controlling a state in the processing chamber based on a temperature condition.
A cleaning wafer or a seasoning wafer is repeatedly used during a lot processing of product wafers. Since a dummy wafer is repeatedly plasma-processed, it is damaged by consumption, or deposits excessively adhered to the surface of the dummy wafer causes contamination of the chamber. To that end, in general, the number of using dummy wafer is limited.
Whenever each dummy wafer is used, the used number of the dummy wafer is counted. If at least one of dummy wafers in a dummy wafer carrier reaches the limited use number, the corresponding wafer is replaced with a new dummy wafer, or the dummy wafer carrier where the corresponding dummy wafer is received is replaced with a new dummy wafer carrier where unused dummy wafers are received. When the dummy wafer carrier is replaced with a new dummy wafer carrier, all of dummy wafers are destroyed even if usable dummy wafers remain in the dummy wafer carrier.
Since, however, one lot includes a plurality of, e.g., 25, product wafers, if dummy processing is required whenever five product wafers are processed, for example, a plurality of dummy wafers is needed until the 25 product wafers of one lot are all processed. Further, the required number of dummy wafers varies depending on a wafer transfer route or a cleaning frequency. When the used number of dummy wafers in the dummy wafer carrier reaches the limited use number before all the product wafers in one lot are processed, the lot processing needs to be stopped in order to replace the dummy wafers or the dummy wafer carrier.
If such circumstances occur during processing of product wafers of one lot, a temperature in the processing chamber or the like is changed before the replacement is completed. Accordingly, the variation in the processing of product wafers in the corresponding lot increases compared to that in conventional lot processing, and this may decrease a production yield.